Metal-Catalyzed Oxidations with Pinane Hydroperoxide: A Mechanistic Probe To Distinguish between Oxometal and Peroxometal Pathways
作者:H. E. B. Lempers、A. Ripollès i Garcia、R. A. Sheldon
DOI:10.1021/jo971270b
日期:1998.3.1
The relative reactivities of tert-butyl hydroperoxide (TBHP) and pinane hydroperoxide (PHP) in metal (Cr, Mo, Ru, Se, V, and Zr)-catalyzed oxidations were compared. When these oxidations involve rate-limiting oxygen transfer from a peroxometal species to the substrate huge differences between TBHP and PHP were observed, e.g., molybdenum-catalyzed epoxidation of cyclohexene with TBHP gave a 98% yield while PHP gave 0%. When the reaction involves reaction of an oxometal species with the substrate as the rate-limiting step, little or no difference is observed, e.g., the selenium-catalyzed allylic oxidation of beta-pinene gave a 96% and 99% yield with TBHP and PHP, respectively. Small but significant differences are observed when reoxidation of the catalyst by the hydroperoxide to the active oxometal species is the rate-limiting step; e.g., the chromium-catalyzed oxidation of carveol gave carvone in 89% and 24% yield with TBHP and PHP, respectively. Hence, the effect of RO2H structure on rate is dependent on the rate-limiting step.